Netty: What is the right way to share NioClientSocketChannelFactory among multiple Netty Clients

Question

I am new to Netty. I am using “Netty 3.6.2.Final”. I have created a Netty Client (MyClient) that talks to a remote server (The server implements a custom protocol based on TCP). I create a new ClientBootstrap instance for each MyClient instance (within the constructor). My question is if I share “NioClientSocketChannelFactory” factory object among all the instances of MyClient then when/how do I release all the resources associated with the “NioClientSocketChannelFactory”?

In other words, since my Netty Client runs inside a JBOSS container running 24x7, should I release all resources by calling “bootstrap.releaseExternalResources();” and when/where should I do so?

More Info: My Netty Client is called from two scenarios inside a JBOSS container. First, in an infinite for loop with each time passing the string that needs to be sent to the remote server (in effect similar to below code)

for( ; ; ){
    //Prepare the stringToSend
    //Send a string and receive a string
String returnedString=new MyClient().handle(stringToSend);
}

Another scenarios is my Netty Client is called within concurrent threads with each thread calling “new MyClient().handle(stringToSend);”.

I have given the skeleton code below. It is very similar to the TelnetClient example at Netty website.

MyClient

import org.jboss.netty.bootstrap.ClientBootstrap;
import org.jboss.netty.channel.socket.nio.NioClientSocketChannelFactory;
public class MyClient {
    //Instantiate this only once per application
    private final static Timer timer = new HashedWheelTimer();

    //All below must come from configuration
    private final String host ="127.0.0.1";
    private final int port =9699; 
    private final InetSocketAddress address = new InetSocketAddress(host, port);
    private ClientBootstrap bootstrap;

    //Timeout when the server sends nothing for n seconds.
        static final int READ_TIMEOUT = 5;

        public MyClient(){
            bootstrap = new ClientBootstrap(NioClientSocketFactorySingleton.getInstance());
        }

    public String handle(String messageToSend){
        bootstrap.setOption("connectTimeoutMillis", 20000);
            bootstrap.setOption("tcpNoDelay", true);
            bootstrap.setOption("keepAlive", true);
            bootstrap.setOption("remoteAddress", address);
        bootstrap.setPipelineFactory(new MyClientPipelineFactory(messageToSend,bootstrap,timer));

         // Start the connection attempt.
            ChannelFuture future = bootstrap.connect();

            // Wait until the connection attempt succeeds or fails.
            channel = future.awaitUninterruptibly().getChannel();


            if (!future.isSuccess()) { 
                return null;  
            }

            // Wait until the connection is closed or the connection attempt fails.
            channel.getCloseFuture().awaitUninterruptibly();

            MyClientHandler myClientHandler=(MyClientHandler)channel.getPipeline().getLast();
            String messageReceived=myClientHandler.getMessageReceived();
        return messageReceived;
    }
}

Singleton NioClientSocketChannelFactory

public class NioClientSocketFactorySingleton {
private static NioClientSocketChannelFactory nioClientSocketChannelFactory;

private NioClientSocketFactorySingleton() {
}

public static synchronized NioClientSocketChannelFactory getInstance() {
    if ( nioClientSocketChannelFactory == null) {
        nioClientSocketChannelFactory=new NioClientSocketChannelFactory(
            Executors.newCachedThreadPool(),
            Executors.newCachedThreadPool());
    }
    return  nioClientSocketChannelFactory;
 }

  protected void finalize() throws Throwable {
    try{
    if(nioClientSocketChannelFactory!=null){    
        // Shut down thread pools to exit.
        nioClientSocketChannelFactory.releaseExternalResources();
    } 
    }catch(Exception e){
    //Can't do anything much
    }
  }
} 

MyClientPipelineFactory

public class MyClientPipelineFactory implements ChannelPipelineFactory {

    private String messageToSend;
    private ClientBootstrap bootstrap;
    private Timer timer;
    public MyClientPipelineFactory(){

    }
    public MyClientPipelineFactory(String messageToSend){
        this.messageToSend=messageToSend;
    }

    public MyClientPipelineFactory(String messageToSend,ClientBootstrap bootstrap, Timer timer){
        this.messageToSend=messageToSend;
        this.bootstrap=bootstrap;
        this.timer=timer;
    }

        public ChannelPipeline getPipeline() throws Exception {

            // Create a default pipeline implementation.
            ChannelPipeline pipeline = pipeline();

            // Add the text line codec combination first,
            //pipeline.addLast("framer", new DelimiterBasedFrameDecoder(8192, Delimiters.lineDelimiter()));
            pipeline.addLast("decoder", new StringDecoder());
            pipeline.addLast("encoder", new StringEncoder());

            //Add readtimeout
            pipeline.addLast("timeout", new ReadTimeoutHandler(timer, MyClient.READ_TIMEOUT));

            // and then business logic.
            pipeline.addLast("handler", new MyClientHandler(messageToSend,bootstrap));


            return pipeline;
        }
}

MyClientHandler

public class MyClientHandler extends SimpleChannelUpstreamHandler { 

    private String messageToSend="";
    private String messageReceived="";


    public MyClientHandler(String messageToSend,ClientBootstrap bootstrap) {
        this.messageToSend=messageToSend;
        this.bootstrap=bootstrap;
    }

    @Override
    public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e){
        e.getChannel().write(messageToSend);
    }

    @Override
    public void messageReceived(ChannelHandlerContext ctx, MessageEvent e){
        messageReceived=e.getMessage().toString();
    //This take the control back to the MyClient
    e.getChannel().close();
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e) {
        // Close the connection when an exception is raised.
        e.getChannel().close();

    }


}

Answer 1

You should only call releaseExternalResources() once you are sure you not need it anymore. This may be for example when the application gets stopped or undeployed.